If you didn't recognise the 'boxy' components, or 'BB' then it sounds like you're on the beginning of a fun journey.
Heed sodderboy's wise words about balancing effort against return and lost magic, but should you decide you prefer modern opamps to 1970s ones, here are two notable points from the plethora of advice around for op-amp swappers:
1. quiescent current draw
It's easy to substitute an OPA134 for a TL071, but it draws twice as much current when idling - get the datasheets and look for "Quiescent Current" or "Supply Current", which is usually quoted as max/min/typical as no two chips are the same. TL071 is 1.4mA - 2.5mA, OPA134 is 4mA - 5mA, the latter being fairly typical for "high-end" audio opamps.
Now calculate worst-case additional load (chips per channel x channel count) and refer to PSU specs (if you have them). You could easily be eating way too far into your PSU's capacity without realising it until too late (smoke/fire/shutdown).
Two solutions: chunkier PSU, or low-current opamps. Circuit traces and bus wiring might not be up to carrying additional current safely: caution advised. The only JFET-input (like TL07x) opamps with v similar current draw and better sonics I found are TI/BB OPA164x (1.8mA - 2.3mA) - but d'oh! they're only available in SOIC so add $2 per chip (for Brown Dog SOIC/DIP adapter), and extra time for soldering the bu%#ers on...
Even though they don't - IMO - "sound good", TL07x are *still* ubiquitous in audio gear because they're stable, measure OK, are cheap as chips
and draw very little current. This means cheaper power supplies, smaller heatsinks, etc.
Replace with OPA1641 and adapter and you're at ~$4.50 per upgraded chip. For comparison, a TL071 is currently around $0.20 in quantity.
2. oscillation
Replace a TL071 with an AD797 (extreme example, bad idea) and it will sing it's heart out at some MHz. You *must* have a scope (faster the better), and 1:10 probe to check whether your opamp replacements haven't just created an expensive high-frequency oscillator. It's like putting a Formula One engine in a Fiat 500: the connections might be similar, but the result could be uncontrollable.
Worse, some part of the circuit - and Aux output, say - might be marginally stable, and only oscillate when something's plugged in, or the opposite - test under as many conditions as you can.
Be organised - make an inventory of all the parts (value and dimensions), cost the various options and test them objectively and subjectively. Fix a budget, and bear in mind you may need additional tools and materials - scope, magnifier, vacuum desoldering pump highly recommended (you'll have hundreds of joints to desolder and clean and a thumb pump won't do), hot air station if SOIC, wipes, DeOxit... Create and print a work sheet/tick list for every channel so you don't lose track, and be in no hurry...
Reworking my desk has been far more time consuming than I anticipated - especially the planning stage. But it's been and educational, enlightening, frustrating, rewarding too. PSUs recapped, cleaned up, and trimmed, Master and Group modules fully complete, 6 of 32 channels done, and I hope to complete by Christmas.
Go for it!
auto
PS thank your luck your ICs have sockets - mine didn't!